1. Field of the Invention
The present invention relates to a fluid coupling to be used in a gas supplying apparatus used in an industrial manufacturing equipment such as a semiconductor manufacturing equipment and, more particularly, to a gas coupling having high gas tightness to be used in an apparatus for supplying a toxic gas.
2. Description of Related Art
In a semiconductor manufacturing process, extremely poisonous gases such as silane, arsine, phosphine, diborane, etc. have been used as dopants which are thermally diffused in a silicon base. Also used is a spontaneous-ignitable gas.
For example, the lethal dose of arsine is 0.5 ppm, and even a little leakage of the gas presents a serious danger to a user. A piping used for these poisonous gases, therefore, has in principle been connected by welding for the purpose of preventing their leakage.
In the meanwhile, for a nonpoisonous gas such as compressed air, pipes to be used are connected by a coupling shown in FIG. 12, not by welding.
In both ends of a through hole made in a body 6 are inserted pipes 5 and 7. On the outer periphery of the body 6 is formed an external screw 6a, which is in engagement with an internal screw 1a formed inside a cap nut 1.
The through hole of the body 6 is largely chamfered on the inlet side; in the chamfered part is fitted a sleeve 12 having a wedge-shaped section. At the center of the sleeve 12 is formed a through hole, in which the pipes 5 and 7 are fitted.
On the bottom face of the sleeve 12 is installed a washer 11 for preventing the sleeve 12 from turning together. The end face on the opposite side of the washer 11 is in contact with the end face inside of the cap nut 1. At the center of the sleeve 12 is formed a through hole, in which the pipes 5 and 7 are fitted.
In a coupling of such a constitution, when the cap nut 1 is tightened to a specific torque onto the body 6, the sleeve 12 is pressed inwardly by the body 6, coming into contact with the outer periphery of the pipes 5 and 7 to deform these pipes 5 and 7.
Thus, the gas tightness of the coupling can be assured by obtaining close contact between the outer peripheral surface of the pipes 5 and 7 and the inner surface of the sleeve 12 and between the outer peripheral surface of the sleeve 12 and the inner surface of the chamfered section of the body.
However, the coupling shown in FIG. 12 has the following problems:
(1) that it has insufficient gas tightness, and therefore is unsuitable for use in piping for poisonous gases;
(2) that it is unremovable without disconnecting the pipes 5 and 7 from the body 6, and therefore, it becomes necessary to provide the piping with a sufficient relief for removal of the coupling; and
(3) that it is likely to be deteriorated in gas tightness at the time of removal and reassembly because the pipe, once jointed, is deformed by compression.
The use of the coupling is required, for example, in connecting the piping with a valve in spite of the above-described problems; the coupling shown in FIG. 12, therefore, is used with an utmost heed in a semiconductor fabricating process where poisonous gases are handled.
However, there has recently been used a coupling disclosed in Japanese Patent Publication No. HEI 2-46830 and other as a means for solving the above-described problems which is capable of maintaining high gas tightness.
A sleeve of this coupling, however, is connected to a pipe of a piping by welding because the sleeve is of a special shape.
Piping connection by welding, however, results in the following problems when poisonous gases are used as a source of dopants to be used for thermal diffusion.
(1) In the course of welding, there occur floating elements, which go as metallic impurities into a wafer, deteriorating device dependability.
(2) Most gases used as a source of dopants have corrosiveness; pipes usually employed are produced of an SUS steel, which is susceptible to a thermal change and corrosion in the welded part by welding. Therefore, there occur particles, which increase a fraction defective due to the presence of a pattern defect.
(3) The welding of SUS steel pipes requires a high welding technique; it has been not easy to employ skilled welding operators in the field of construction of a semiconductor manufacturing process.